The front brake of my 1978 Honda CB400A (baby cafe racer -- AKA "decaf") went almost dead. Here, we fix it in about 30 minutes -- my first time doing more than just an oil change or electronic reworkings! 8-)
We assume somehow my brake fluid has deteriorated/aged from viscous fluid to closer to water (this naturally happens over time) and/or somehow has taken in air (which will sack your brakes entirely).
We open my brake master cylinder, inspect, flush clean brake fluid through (making sure to never get air into the line -- AKA "brake bleeding"), and see how the results are.
I get some advice and much wanted help from the experienced moto-wrench, twin brother, Russ AKA "Green Magic Man".